I can't really categorize this as advertising, but I came across some really great thinking done by the design group INOUT. They define themselves as "a promotional platform bringing young creative people together by means of exhibitions, publications and productions." The following examples let you "experiencing the city through the eyes of these designers."

6 bicycles versus 1 car. A critical proposal for urban planning.

"This water collector invites all the animals that inhabit our towns and cities to come and slake their thirst."

"These days, a fountain no longer really serves any useful purpose beyond its decorative appearance. here a mirror permits it to be transformed into an outdoor bathroom."